Determination of lactate threshold by respiratory gas exchange measures and blood lactate levels during incremental load work.

OBJECTIVE: The purpose of this investigation was the determination of the lactate threshold (LT) by selected respiratory gas exchange measures and venous blood lactate levels during incremental load work on a mechanically braked cycle ergometer. DESIGN: Repeated measures design. SETTING: Human Performance Laboratory. PARTICIPANTS: Eight healthy trained soccer players (mean age 21.9 +/- 3.0 yr, mean VO2max = 59.2 +/- 3.6 ml.kg.min-1). OUTCOME MEASURE: Subjects conducted two incremental load work tests. Incremental load work was increased by 1 kilopond (kp) every third minute at 60 rpm until voluntary exhaustion. Blood samples from a forearm vein were collected during the second trial (T2) only and analyzed for lactic acid [LA-]. RESULTS: One-way analysis of variance (ANOVA) with repeated measures indicated no statistically significant difference between the two tests for maximal oxygen uptake (VO2max), maximal carbon dioxide production (VCO2max), maximal heart rate (HRmax), maximal pulmonary ventilation (VEBTPSmax) and lowest ventilatory equivalent of oxygen (VE/VO2), respectively; however, there was a significant difference among the oxygen uptake (VO2) values at the LT for the four determination methods. In our subjects, the measured (mean +/- SD) VE/VO2 in relation to VO2 for the first trial (T1) of 22.9 +/- 1.9 occurred at VO2 of 1.27 +/- 0.8 l.min-1. The lowest VE/VO2 and the onset of [LA-] accumulation calculated from individual exponential equations relating VE to VO2 yielded VO2 values of 1.77 +/- 0.18 and 1.74 +/- 0.25 l.min-1 for the T2. Utilizing natural log for lactate ln [LA-] to natural log for ln (VO2) equations, the LT for T2 occurred at VO2 of 1.30 +/- 0.70 l.min-1. CONCLUSION: LT was best predicted by the measured lowest VE/VO2 and the plot of the ln [LA-] to ln VO2 relationship. The methods used in this study provide a valid estimate of the LT and support the use of measured lowest VE/VO2 as an indirect measure of the LT.

Interrelationship between plasma potassium concentration, pulmonary ventilation and electrocardiographic change during and after highly intense exercise.

OBJECTIVE: The purpose of this investigation was to induce elevated plasma concentrations of potassium (K+) efflux from active muscle cells during intense muscular exercise. The relationship between K+, pulmonary ventilation (VE) and EKG changes, specifically T-wave amplitude, is presently controversial. DESIGN: Repeated measures design. SETTING: Human performance laboratory. PARTICIPANTS: Twelve volunteer trained recreational cyclists (10 males, mean age 31.9 +/- 7.4, and 2 females, mean age 27.5 +/- 0.7, mean VO2max 571.2 +/- 6.4 ml.kg.min-1). OUTCOME MEASURE: Subjects performed 10 min of pedaling at 90 rpm, yielding a power output of 45 W.min-1 on a mechanically braked cycle ergometer as a warm-up. Each exercise stage was 2 min in duration, beginning at 135 W and increased by 45 W thereafter until voluntary exhaustion. Respiratory gas exchange measures were obtained every 10 sec. Venous blood samples for K+ and lactate (LA-) determination were drawn at rest, at the end of stage 2, all subsequent stages, and during 3 and 10 min of recovery. EKG recordings were concurrent with venous sampling. RESULTS: Statistical analyses for VE vs. K+, respiratory exchange ratio (RER) vs. K+ and RER vs. LA- revealed neither significant change nor an associative relationship from stages 1-3. However, stages 4-8 were statistically significant (p < .05) and highly correlated. No relationship was found between K+ change and T-wave amplitude during exercise or recovery. CONCLUSION: These data indicate a strong relationship between selected respiratory gas exchange measures and K+ during intermediate to highly intense exercise.